Conventionally, a so-called parallel link type industrial robot has been known as an industrial robot for conveying a work such as an electronic component (see, for example, Patent Literature 1). The industrial robot described in Patent Literature 1 includes a main body part, three levers which are turnably connected with the main body part, three sets of parallel links which are respectively connected with three levers, and a movable part connected with three sets of the parallel links. The three levers are connected with the main body part so as to extend substantially radially at a pitch of 120° toward an outer peripheral side of the main body part and a drive mechanism for turning the lever is connected with each of the three levers. The movable part is, for example, provided with a holding mechanism for holding a work.
In a connecting part of the main body part with the lever in the industrial robot, the lever is connected with the main body part so that the lever is capable of turning relative to the main body part with a direction substantially perpendicular to the direction where the lever is extended from the main body part as an axial direction of the turning. In a connecting part of the lever with the parallel links, the lever and the parallel links are connected with each other by a three-axes ball socket joint structured of a ball for a joint and a joint socket which is formed with a recessed part where the ball is accommodated. Further, in a connecting part of the parallel links with the movable part, similarly to the connecting part of the lever with the parallel links, the parallel links and the movable part are connected with each other by a three-axes ball socket joint. A tension coil spring for urging the recessed part of the joint socket toward the ball is disposed between the parallel links in the connecting part of the lever with the parallel links and in the connecting part of the parallel links with the movable part.
The industrial robot described in Patent Literature 1 which is structured as described above is capable of holding a work disposed at an arbitrary position by the movable part and conveying in an arbitrary direction, i.e., an upper and lower direction, a front and rear direction and/or a right and left direction in a predetermined area.